
Indigo leaves need to soak in covered warm water until the color of the liquid turns to antifreeze and leaves have a fermented, fruity smell. It helps to weight down the leaves, as they will pop up above the water.

When the liquid from fermented leaves turns this color, it’s time to remove the leaves, add an alkaline substance, historically slaked lime (or pickling lime), and agitate the bath. This is before agitation or the addition of lime.

Once the liquid has been aerated (beaten with a whisk, poured between containers or agitated with an immersion blender), you it will froth and foam and turn blue.
The amount of slaked lime added is 1 tsp per 1 gallon of liquid.